The railway track usually comprises a track bed (with ballast or without ballast), a sleeper and a rail. The track bed is formed on the subgrade or bridge, the sleeper is laid on the track bed, and the rail is installed on the sleeper.
The material of the sleeper used in the earliest ages is wood, so also called the sleeper wood. The wood has good elasticity and insulation ability, low sensibility to the variation of temperature around, light in weight, easy machining and replacement, and enough displacement resistance. After preservative treatment, the service life of the wood sleeper can be greatly prolonged, may be as long as about 15 years. So 90% of railway in the world was using the wood sleeper. According to the statistics, during the peak period of wood sleeper used, more than 3 billion wood sleepers were laid all over the world, and most of them are pines.
With the decreasing of forest resources and strengthening of people's environment protection consciousness, and also benefit from the great development of science and technology, in the early 1900s, some countries began to produce the steel sleeper and reinforced concrete sleeper to replace the sleeper wood. However, because the steel sleeper consumes a large amount of metal, is expensive and heavy, it is not widely used, only a few countries such as Germany are still using the steel sleeper. Since 1950s, most of the countries in the world began to produce the reinforced concrete sleeper, which has long service life, high stability, low quantities of maintenance, and broken rate and rejection rate being greatly lower than that of the wood sleeper. On a continuous welded rail track (track laid with welded long rails, named due to no seam on a long rail), the stability of reinforced concrete sleeper is improved average 15-20% than that of wood sleeper, so, especially suitable for high speed passenger railway line, such as Japan's Shinkansen, China's high speed dedicated passenger railway line, and Russia's high speed railway line.
However, no matter what the material of sleeper was used, most of railways have adopted the transverse sleeper at present. That is, the sleeper is laid transversely along the track or rail. This transverse sleeper has many disadvantages and shortages.
The transverse sleeper is laid separately on the track bed, so it is unfavorable for distribution of load from rail. When a train passing, under the impact of wheels, the sleeper shall suffer high impact load, easily cause damages to track bed underneath, such as ballast broken, and displacement, thus after a long period of using, the rail may deform and cause the traveling of train vibrated and swayed, give serious and adverse influences to the train running stability and riding comfortability. On the contrary, the train vibration and swaying will speed up the worsening of railway conditions.
The railway maintenance is a kind of hard labor. If the railway track deformed (mainly the deformation of rail), or concrete sleeper fractured, a great amount of resources shall be paid for correcting the deformation of rail, or repairing the fracture of concrete sleeper. In addition, it requires frequent maintenance for ballast broken or displaced.
Recently, to overcome such many defects and shortage of traditional transverse sleeper, it has been put forward a longitudinal sleeper (also called “trapezoidal sleeper” or “ladder-type sleeper” in some documents), this longitudinal sleeper comprises both parallel longitudinal prestressed concrete beams laid longitudinal along a railway, and a steel pipe connecting between both longitudinal beams.
As an example, CN1135279C discloses a typical longitudinal sleeper (or trapezoidal sleeper), which comprises a pair of longitudinal beams made of prestressed concrete, two rails respectively arranged longitudinally on the pair of longitudinal beams; and a plurality of steel pipes used as connectors being arranged along the rail horizontally in the specified spacing, for connecting the pair of longitudinal beams and keeping the rail gauge. The longitudinal beam has the internal pre-tensioned rebar to increase the strength of the longitudinal prestressed concrete beam, and prevent its fracture. Both ends of the steel pipe are respectively preburied in the pair of longitudinal beams, and intersected with the rebar in the longitudinal beam. The longitudinal prestressed concrete beam is preburied with a plurality of fasteners (usually sleeves) for installing the rail onto the sleeper by interconnecting between the fasteners and clamping pieces. To prevent the steel pipe turning or displacing between the longitudinal prestressed concrete beams, both ends of the connector (i.e., steel pipe) is provided with a rib being radially projected to transfer the torsion of the connector to the concrete. These ribs still have small ribs on top and bottom surfaces to transfer the transverse force from the connector to the concrete.
In the aforesaid type of longitudinal sleeper, because the longitudinal beams are continuously arranged longitudinally along the rail, so greatly improve the distribution of train loads, effectively control the deformation of rail, greatly save the railway maintenance cost.
In addition, CN1167183A also relates to a longitudinal sleeper, which mainly improves the end of the steel pipe for connection with the longitudinal beam, that is, makes the end into flat shape, thus prevent the turning and withdrawing of the steel pipe through a simple structure (no rib and the like required). In addition, filling concrete into the steel pipe may increase its bending strength.
Obviously, compared with the traditional transverse sleeper, the above mentioned longitudinal sleeper has many advantages. However, the prior longitudinal sleeper still has some shortages. For example, the steel pipe for connection with a pair of longitudinal beams may interfere with the electrical signal of a train. In addition, if exposed outside for a long period of time, the protective paint on the surface of the steel pipe may be peeled off and then the pipe may be eroded. In order to protect the paint from being peeled off, some protective measures should be taken during the transportation and construction, thus the transportation and construction difficulty shall be increased, and so the labor for maintenance and cost. So, it is necessary to improve the prior longitudinal sleeper.